Method of producing bulked, highly stretchable, textured cotton yarns from blends oftreated and untreated cotton fibers, using a deferred curing process



United States Patent "aw-mm m...

ABSTRACT OF THE DHSCLQSURE Scoured cotton fibers treated with a crosslinking-type resin having a low rate of cure under ambient conditions of temperature and humidity are dried, but not cured. The treated fibers are blended with various percentages of untreated fibers. Plied yarns spun from these blends are then permanently crimped by heat setting at high temperatures and then reverse twisted. Highly stretchable, crosslinked cotton yarns are produced. The bulk, stretch, and other properties of the textured cotton yarns will vary depending upon the percentage of resin-treated and untreated fibers blended together, and the resin add-on of the treated fibers.

These textured yarns have particular utility in the manufacture of upholstery, rugs, and certain items of wearing apparel where yarns with considerable bulk, and good stretch and stretch recovery are required.

mor A non-exclusive, irrevocable, royalty-free license in the invention herein described, throughout the world for all purposes of the United States Government, with the power to grant sublicenses for such purposes, is hereby granted to the Government of th- United States of America.

FEELD OF THE INVENTEON This invention relates to the production of cotton yarns that exhibit high stretch and subsequent recovery from stretch characteristics, together with inherent bulk. More specifically, the invention deals with an improved method for producing highly stretchable, crossli ked cotton yarns by a deferred curing process. Still more specifically, the invention deals with a method of treating a portion of the cellulosic fibers with a deferred-cure crosslinking agent prior to the formation of a singles yarn. The resultant yarns have latent fiber mobility. When these singles yarns are converted into plies of a plurality of these singles yarns, and subsequently are cured and reverse twisted, improved strength, stretch, stretch recovery, and abrasion resistance are imparted to the textured yarn.

PRIOR ART In US. Patent 3,127,737. a method is described for producing bulked, highly stretchable, textured cotton yarns wherein the cotton staple is first converted into a single yarn having suitable Z (or S) twist. These singles yarns are then converted into plied yarns (2 or more singles yarns) by twisting in the same direction as the twist in the singles yarns (Z or S) to form a tightly twisted plied yarn. The yarns are then impregnated with a solution comprising a cross linking type resin and a catalyst for said resin. Subsequent drying and curing sets the twist in the yarn. The treated yarns are then reverse twisted (sometimes termed backtwisted), preferably past zero ply twist.

The backtwisted yarn, when relaxed, tends to return to the position in which it was set when the resin was ice cured. The component yarn strands separate and the relaxed, bncktwisted resintreatcd yarn takes on the appearance of multiple, helical coiled springs, each yarn strand forming coils in the direction of the backtwist.

This method of producing highly stretchable textured cotton yarns has some disadvantages. in the first place, for those commercial processors who may handle large quantities of highly stretchable textured cotton yarns, drying the resin treated cellulosic yarns presents the serious problem of resin migration. This migration problem can be minimized by converting the yarns into packages and then treating with the resin solution in a package dyeing machine to give suitable resin pickup. The packages of yarn are then transferred to a dielectric oven where drying and curing are accomplished. This is a very expensive operation.

In the second place, a large inventory of the treated cotton stretch yarns is required because each bulked, highly stretchable cotton yarn requires singles and plied yarns having specific construction such as twists per inch, direction of twist (Z or S), and number of singles per plied yarn. As noted above this requires a large inventory of treated yarns.

In the third place, when the highly-stretchable, textured cotton yarns are to be dyed, this operation must be ried out prior to the application of the resin. This adds another requirement to those mentioned above, and increases the expensive inventory accordingly.

We have now discovered that the above disadvantages may be overcome by the following general procedure:

(a) Opened cotton fibers, preferably scoured and bleached cotton fibers, are treated with an aqueous solution of a deferrethcure crosslinking resin and a catalyst suitable for said resin. A dye may be: included in the eating solution.

Crosslinking agents suitable for use in the practice of our invention include reagents that contain two or more functional groups that are capable of reacting with the cellul se or with themselves. Two types of crossiinking agents have caused excellent results to be obtained, namely, essentially monomeric, thermosetting, crosslinking agents and essentially monomeric, thermoplastic, crosslinking agents. We prefer the monomeric thermosetting crosslinking agents.

Typical examples of commercially available, essentially monomeric thcrmosctting, crosslinking' agents are N,l-ldimethylol-4,5-drnydroxy cyclic ethyleneurea, diinethylol hydrox ethyl carbamate, bis-methoxymethyl ethylcarbar-hate, vinyl cyclohexanediepoxide, acetals, and rela ed crosslinking agents that have a slow rate of cure (long shelf life) under ambient conditions of temperature and humidity.

Regardless of the resin used, the concentration of the crosslinking agent in the treating bath should be adequate to deposit about from 1 to 20 weight percent dry resin add-on after the fibers have been dried, and equilibrated. Usually, concentrations of about 1 to 28 weight percent on the weight of the solution (OWS) with a subsequent wet pickupof about to weight percent on the weight of the fiber (OWF) is a good practice.

Catalysts suitable in this invention are those commonly used with the thermosetting resins. Typical examples include zine nitrate, zinc fluoroborate, soluions of zinc salts buffered with organic acids such as acetic acid, nesium chloride, and similar acid or latent acid catalysts. Latent acid catalysts refer to products which become effective at curing temperatures. However, in order to be suitable for the practice of the present invention, these catalysts must be neutralized, or buffered, where necessary, so that the aqueous crosslinking solution containing the catalyst is neutral, or only slightly acidic. In general, it is areferred that the pH of the aqueous crosslinking solution e in the range of 3 to 7. Low pHs, i.e., about 2 or lower, are not suitable because of the increased susceptibility of the crosslinked, uncured fibers to cure" during the subsequent conventional cotton processing, or storage. Also, there is a potential danger of acid-tendering of the treated fibers. Alkaline p-Hs, i.e., above 7, are likewise unsuitable. A particularly suitable pH range for the aqueous crosslinking solution of the present invention is 5 to 7, preferably 56.5. The adjustment of the pH of the latent acid-forming catalysts, zinc nitrate, and magnesium chloride, to produce the aqueous crosslinking solution having a pH of 6.5 or slightly lower may be accomplished by the addition of any compatible alkaline agent, or by the use of buffers. The zinc nitrate catalyst should not be buffered or neutralized to above a pH of 6.5 to avoid precipitation of water-insoluble, noncatalytic zinc hydroxide. Should this precipitate appear, addition of a few drops of acetic acid is usually suificient to reduce the pH of the aqueous crosslinking solution to a pH below 6.5 and prevent the formation of zinc hydroxide.

The amount of catalyst employed will depend upon the amount of crosslinking agent. However, amounts ranging from about 0.5 to 5 weight percent (V is a good practice for the thcrmosetting crosslinking agents. The particular catalyst to be used with a particular crosslinking agent is known to those skilled in the art.

Auxiliary agents suitable for use in this invention are softeners, wetting agents, optical whiteners, reactive dyes, lower alkyl alcohols, such as ethyl and isopropyl alcohols, methyl ethyl ketone, dimethyl formamide, and other commonly used finish modifiers.

A typical example useful in the practice of this invention comprises 12 weight percent dimethylol dihydroxy ethyleneurea; 0.2 weight percent wetting agent; 1.0 weight percent dye; 3.0 weight percent alcohol, methyl ethyl ketone, dimethyl formamide, and the like; and the balance water, all percentages (OWS).

Typical wetting agents are ethyl, methyl, and isopropyl alcohols; nonionic agents such as alltylaryl polyether alcohols, alkylaryl polyglycols, and the like.

Typical dyes are optical whiteners, and reactive dyes such as Reactive Red 12, Reactive Violet 2, Reactive Yellow 6, Reactive Blue 5, and the like.

Typical softening agents are polyethylene, polypropylene, and the nonionic fatty ester-amides. These auxiliary agents are not limiting features of this invention.

TREATING THE COTTON FIBERS As noted above, cotton fibers, preferably scoured and bleached, are passed into, and through, the aqueous bath comprising the treating agent and catalyst. The fibers may be in bulk form, or they may be in the form of a pickerlap enclosed (encased) in scoured and bleached cotton gauze. The gauze tends to hold the lap in position and simplifies the treating operation. We prefer the use of fibers in the form of a 13 oz./yd. picker-lap enclosed in bleached cotton gauze.

A period of dwell (residence time) in the aqueous treating bath is maintained for sufficient time to permit the aqueous treating bath to penetrate the individual fibers. When unscoured fibers are used, a wetting agent may be added. It is also within the scope of our invention to add a softening agent and/or a dye.

(b) Excess resin solution is then removed to give a wet pickup of about 85 to 110 weight percent (OWE). This may be accomplished by use of a centrifuge, or other suitable means. We prefer the padder rolls.

Should one pass of the fibers through the resin treating bath be insutficient to give a 'WBlI pickup of about 85 to 110 weight percent, the treatment should be repeated. The dry resin addon should be about 1042 wcight percent on the Weight of the untreated fibers.

(c) The treated fibers are then dried at a temperature not over about 200 F., to a moisture content not less than about weight percent. These drying conditions are critical in this invention.

(d) The dried fibers are then permitted to equilibrate at ambient temperature and humidity to reduce the moisture about from 5.5 to 8.0 weight percent. After equilibration, the treated fibers are flexible, pliable, and may be readily processed on the equipment used in conventional cotton systems. The equilibrated fibers may contain about from 1 to weight percent (OWE) dry crosslinlzing agent, preferably 10 12 Weight percent based on the weight of the untreated fiber.

(e) Resin treated and untreated fibers are then lended together in such proportions as -75%, 50%, and -25% treated/untreated fibers respectively.

(f) The blended fibers are then processed into singles yarns having suitable Z (or S) twist. As noted above under step (c) the dried, resin-treated fibers after equilibration are flexible, pliable, and may be readily processed on the equipment used in conventional cotton s sterns.

(g) These singles yarns are converted into plied yarns (two or more singles yarns) by twisting in either the Z on Z direction or S on 3 direction to form a tightly tvisted plied yarn.

(h) The highly twisted yarns are then heat cured. This is accomplished by giving the yarns a heat treatment at about 350 F. to 400 F. for about 10 seconds to 3 seconds (or other appropriate time intervals dependent on the temperature) to complete the crosslinking between the treating agent and the cellulose.

This heat treatment (or delayed cure) is a critical feature of our invention and only crosslinking agents that have good shelf life at ambient room temperatures and humidities are useful in the proces of our invention.

(i) The treated and cured yarns are then twisted in the reverse direction, preferably past zero ply twist.

Since the deferred-cure type crosslinking resins remain stable in storage for long periods of time, the fibers can be treated, dried but not cured, equilibrated and then held in storage. When an order for a particular construction of yarn is received, the treated fibers are blended with the proper percentage of untreated fibers and the blend is processed into stretch yarns of the particular specifications required, thereby reducing the necessity for large inventories of treated cotton stretch yarns. Also, since the resin is applied to the fibers and dried before processing into yarns, the problem of resin migration is eliminated.

It is within the scope of our invention to heat-cure and reverse-twist the highly-twisted plied yarns in a continuous operation. To accomplish this the yarns are passed through the heater tubes and directly to the backtwister. The speed of the yarn, temperature, and length of the heater, the turns per inch of the applied yarn and the turns per inch of the reverse twist for a 13.5/2 yarn listed in Example 1 are satisfactory for such a continuous operation.

The bulk and the stretch of the cotton yarns that are the subject of this invention are controlled by varying the amount of twist in the component yarns, the amount of twist prior to heat-curing, and the amount of reverse twist after the yarn has been set by heat-curing the resin. For a given yarn size, the size of the helical coils in the relaxed yarn is governed to some extent by the amount of twist in the original yarns that go into the plies. As the twist of the singles is decreased, the coils become larger and the yarn can be straightened by less tension. The amount of ply twist and reverse twist (backtwist) given to the yarn controls the number of coils, the number of coils per inch increasing with increasing twist.

The following are detailed descriptions of methods for producing the products of our invention. As will be apparent to those skilled in the art, either a Z twist or an S twist can be used in the singles yarn at the start. If S twist singles are used, these may be plied with an S twist on top of the S twist singles, and then reversetwisted past zero after the resin is cured.

EXAMPLE 1 Scoured and bleached cotton fibers in the form of picker-lap were treated with a 13% aqueous solution of N,N-dimethylol-4,S-dihydroxy cyclic ethyleneurea which solution contained in addition 0.27% alkylaryl polyglycol, 3.25% of ethyl alcohol, 0.5% buffered zinc nitrate catalyst, and 1.0% brown dye. A wet pickup of approximately 86% was used, resulting in a resin add-on of about 10.4%. /The fibers were dried at 200 F. to a moisture content about from to 12%. After equilibration at ambient temperature and humidity to reduce the moisture content to about 5.5 to 8.0 weight percent (OW F) the treated fibers were then blended with scoured and bleached, but otherwise untreated, cotton fibers in the following proportions: 75% untreated and treated, untreated and 50% treated, 25% untreated and treated. Each of the blends of fibers was subsequently processed into 13.5/1 yarn (singles) using a 3.5 twist multiplier, Z twist (approximately 13 turns per inch), and plied in a 2" twist (twist-on-twist) direction using a 7. 0 twist multiplier (approximately 18.2 turns per inch). The highly twisted yarns were heat-cured at the rate of 10 yards per minute at 380 F. in a 30-inch long heater tube and then back-twisted on a conventional twister approximately 39 turns per inch in an S twist direction. The following table shows the stretch properties of yarns made from each of the three a*bove-mentioned blends.

The procedure of Example '1 is repeated except dimethylol hydroxyethyl carbamate is used in place of N,N-dimethylol-4,S-dihydroxy ethyleneurea. Again, the percent stretch of the reverse-twisted fibers increases as the ratio of treated fibers to untreated fibers increases.

EXAMPLE 3 The procedure of Example 1 is repeated except his methoxyrnethyl ethylcarb-amate is used in place of N,N- dimethylol-4,5-dihydroxy ethyleneurea. Again, the percent stretch of the reverse-twisted fibers increases as the ratio of treated fibers to untreated fibers increases.

The brown dye used in the above examples consists of 58 parts Reactive Brown 1, 38 parts Reactive Red 12, and 4 parts Reactive Black 1. Parts are by Weight.

We claim:

1. A process for producing stretchable cotton yarns comprising the following operations to be carried out in sequence: resin treating cotton 'fibers with a delayedcure, crosslinking type textile treating resin, and a catalyst suitable for said resin; removing the excess resin solution to give a wet pickup about from to percent by weight on the weight of the fiber; drying the treated fibers at a temperature no greater than about 200 F. to a moisture content no less than about 10 weight percent; equilibrating the dried fibers at ambient temperature and humidity to reduce the moisture to about 5.5 to 8 weight percent; blending resin treated fibers with untreated fibers; processing the blended fibers into singles yarn; plying singles yarns of the same directional twist into plies of a plurality of singles yarns, the plied yarns having the same directional twist as the singles yarns from which they are made; heat treating the plied yarns to cure the resin and set the initially installed and inherent twist in the plied yarns; and thereafter reverse-twisting the delayed-cure, resin-treated and heatcured yarns.

2. The process as defined in claim 1 wherein the re verse twist of the plied yarn and heat treatment of the delayed-cure resin are accomplished in a continuous operation.

3. The process as defined in claim 1 wherein the delayed cure resin is selected from the group of crosslinking resins consisting of N,N dimethylol-4,5 dihydroxy cyclic ethyleneurea, dimethylol hydroxyethyl carbamate, bis-methoxy-methyl ethylca'rbamate, and vinyl cyclohexanediepoxide.

4. The process as defined in claim 3 wherein the delayed-cure resin is N,N-dimethylol-4,5-dihydroxy cyclic ethyleneurea in an amount sufllcient to provide a resin add-on of about 10 to 12% by weight based on the weight of the untreated plied yarn.

References Cited UNITED STATES PATENTS 3,127,732 4/1964 Brown et a1. 57 164 JOHN PET'RAKES, Primary Examiner. 

